Hi Jocelyne and everyone,
You asked about a banking term. Since I’m no banker, I didn’t know this terminology in English, let alone in French!
But at long last, here's the translation:
“He must be at a client meeting.”
That's always appropriate to say. But in some cases, depending on the circumstances, a person may prefer to say:
“He must be attending a client meeting.”
Happy week, everyone!
Mathea